Encrypt some stream on hte fly using AE (EtA) with SHA256-based HMAC. Caller must call
EtaEncryptingStream#close() in order to properly finish
AE process. Note, to get the maximum security you should put some random sized random data in
the file. As a variant, write some number N and then N random bytes. Have N also random. When
reading, read N and skip N bytes first. Otherwise, use
to write structured data and put some random bytes in the beginning then skip it.